How to make NPC wander randomly/follow you and run away if you get too close?

create a StringValue inside the NPC called "NpcMode"

this script will make it move around if the value is Normal

local CurrentPart = nil
local MaxInc = 16

function onTouched(hit)
    if hit.Parent == nil then
        return
    end

    local humanoid = hit.Parent:findFirstChild("Humanoid")

    if humanoid == nil then
        CurrentPart = hit
    end
end

function waitForChild(parent, childName)
    local child = parent:findFirstChild(childName)

    if child then
        return child
    end

    while true do
        print(childName)

        child = parent.ChildAdded:wait()

        if child.Name==childName then
            return child
        end
    end
end

local Figure = script.Parent
local Humanoid = waitForChild(Figure, "Humanoid")
local Torso = waitForChild(Figure, "Torso")
local Left = waitForChild(Figure, "Left Leg")
local Right = waitForChild(Figure, "Right Leg")

Humanoid.Jump = true

Left.Touched:connect(onTouched)
Right.Touched:connect(onTouched)

while true do
    wait(math.random(2, 6))

    if CurrentPart ~= nil and script.Parent.NpcMode.Value == "Normal" then

        Humanoid:MoveTo(Torso.Position + Vector3.new(math.random(-MaxInc, MaxInc), 0, math.random(-MaxInc, MaxInc)), CurrentPart)
    end
end

and if the value is attacking, this script will make it chase the nearest Player

wait()
zombieParent = false

while zombieParent == false do

    wait()
    if script.Parent.NpcMode.Value == "Attacking" then
        zombieParent = true
    end

end

local larm = script.Parent:FindFirstChild("Left Arm")
local rarm = script.Parent:FindFirstChild("Right Arm")
local waitTimer = 0

function findNearestTorso(pos)
    local list = game.Workspace:children()
    local torso = nil
    local dist = 10000
    local temp = nil
    local human = nil
    local temp2 = nil
    for x = 1, #list do
        temp2 = list[x]
        if (temp2.className == "Model") and (temp2 ~= script.Parent) then
            temp = temp2:findFirstChild("Torso")
            human = temp2:findFirstChild("Humanoid")
            if (temp ~= nil) and (human ~= nil) and (human.Health > 0) then
                if (temp.Position - pos).magnitude < dist then
                    torso = temp
                    dist = (temp.Position - pos).magnitude

                    if human.Health >= 1 then 
                    script.Parent.Range.Value = true 
                    else 
                    script.Parent.Range.Value = false 
                    end 
                end
            end
            if dist < 10 then 
                script.Parent.Attack.Value = true 
            else 
                script.Parent.Attack.Value = false 
            end 
        end
    end
    return torso
end

function Sit()
    if script.Parent.Humanoid.Sit == true then 
        script.Parent.Humanoid.Jump = true 
        print("Anti Seat Putter!!!")
    end 
end

script.Parent.Humanoid.Changed:connect(Sit)

while true do
    wait(1)
    local target = script.Parent.Target.Value
    if target ~= nil then
        rx = math.random(-3,3)
        ry = math.random(0,0)
        rz = math.random(-3,3)
        script.Parent.Humanoid:MoveTo(target.Position+Vector3.new(rx,ry,rz), target)
    else 
    end
end

oh, and create a StringValue with the "Target" name, the Npc will always chase the Player with his name in the Target value

please, if this help you, make as answer, thanks.

The main actions you want the NPC to perform are based on the distance from the player, so you'll need .magnitude for this.

For my example, I am adding an IntValue named "FarAway" inside the script so that you can get the magnitude set continuously and be able to activate the movement based on it.

local player = game.Players.LocalPlayer
workspace:WaitForChild(player.Name)

local npc = workspace.NPC
local humanoid = workspace.NPC.Humanoid
local debounce = true

script.FarAway.Changed:Connect(function()
if debounce == false then return end

local distance = script.FarAway.Value
    if distance > 10 and distance <= 25 then
        local randomx = math.random(-25, 25)
        local y = npc.HumanoidRootPart.Position.Y
        local randomz = math.random(-25, 25)
        npc:MoveTo(player.Character.HumanoidRootPart.Position + Vector3.new(randomx, y, randomz))
        humanoid.MoveToFinished:Wait()
    elseif distance > 25 and distance < 50 then
        debounce = false
        npc:MoveTo(player.Character.HumanoidRootPart.Position + Vector3.new(0, 0, 10))
        humanoid.MoveToFinished:Wait()
        debounce = true
    elseif distance >= 50 then
        debounce = false
        local randomx = math.random(-100, 100)
        local y = npc.HumanoidRootPart.Position.Y
        local randomz = math.random(-100, 100)
        npc:MoveTo(npc.HumanoidRootPart.Position + Vector3.new(randomx, y, randomz))
        humanoid.MoveToFinished:Wait()
        debounce = true
    end
end)

while true do
    script.FarAway.Value = (player.Character.HumanoidRootPart.Position - npc.HumanoidRootPart.Position).magnitude
end

I also added a debounce for the movements that are not too close to the player so that they can finish firing. If the player is too close, there is no debounce so that the random path the NPC takes is not continuously towards the player.